Pistons



M. KUHM PISTONS March 30, 1965 Filed Dec. 20, 1962 F ig. I

Jnven/Dr:

MX Kwm United States Patent PISTONS Max Kuhm, Neckarsulm, Wurttemberg, Germany, assignor to Karl Schmidt G.m.b.H., Neckarsulm, Wurttemherg, Germany, a German corporation Filed Dec. 20, 1962, Ser. No. 246,259

Claims priority, application Germany, Dec. 28, 1961,

Sch. 30,760

8 Claims. (Cl. 92-228) This invention relates to light metal pistons, and has as its object to provide improvements in piston construction.

Pistons made of light metal, e.g. light metal alloy, are presently used almost exclusively in quietly running engines. Rings or strips of metal of low thermal expansion, made preferably of ferrous metals, are installed in such pistons so that the barrel of the piston is deformed in a specific manner when its temperature rises.

There are several known systems for producing an appropriate deformation of the barrel of such pistons.

Light metal pistons with temperature compensators are manufactured with a highly ovalized shape, i.e., the diameter of the barrel along the axis of the wrist or piston pin is as much as 0.5 mm. shorter than the diameter perpendicular thereto. As the piston becomes hot, the in serted compensators of low thermal expansion transform the oval shape of the barrel to a round or approximately round shape. In this manner, the greater thermal expansion of the light metal piston is directed parallel to the piston pin, while its thermal expansion perpendicularly to the pin is restricted, and corresponds largely to the thermal expansion of the iron cylinder.

Furthermore, pistons with steel inserts of the abovenamed kind, hereinafter briefly called compensated pistons, have the advantage that they are much less susceptible to piston seizure than are light metal pistons without steel inserts. This is because, in the compensated pistons, the drawing in of the upper portions of the sides of the piston that are subject to side thrust can be regulated by the steel members in such a manner that the clearance between the piston and the iron cylinder remains unvaried in the various states of operation and at the various temperatures encountered.

In compensated pistons, based on the above principle, this deformation of the piston barrel is obtained by use of internally disposed semicircular strips of steel whose centers are on the wrist pin axis. In effect, bi-metallic bodies bend the wall of the piston when the piston is heated. These bi-metallic members perform each a pincer-like action to force the piston toward circular form.

In present day engines the load per unit of displacement is constantly increasing in terms of mean pressures and revolutions per minute, and at the same time there is an increasing demand for quietness of operation, perfection of seal, and long service life. Hence, pistons must be fitted with the greatest precision in order to meet present requirements. The invention is particularly directed to fulfilling these requirements.

The piston barrel constructed according to the invention differs basically from the known designs in that on the sides subject to lateral thrust, i.e., on the sides which contact the walls of the cylinder in the plane of oscillation, the piston skirt is thickened. By reason of such construction, in the compensating action which occurs when the piston temperature rises, no, or substantially no deformation occurs at the thickened areas of the piston skirt. As soon as the body of the piston is heated to higher temperatures, four compensating inserts or strips curve progressively inward, thus pulling the thickened segments inward, and these segments remain parallel to the cylinder wall and retain their geometrical shape. At the same time, the piston barrel expands in the direction of the bosses, and thus, its natural thermal expansion is channeled exclusively, or substantially exclusively, in a known manner, in the direction of the bosses. The inserts can be of the type used in known compensating pistons.

Thus, the invention provides an oval piston comprising a hollow piston body of a light metal of relatively large thermal expansion and having wrist pin bosses for receiving a wrist pin for the piston. A circumferentially extending segment of the piston wall intermediate the wrist pin bosses is relatively thick, and there is a relatively thin circumferentially extending wall segment between the thick segment and each of the Wrist pin bosses. There is one thin segment on each side of the thick segment. An insert of material of relatively small thermal expansion is bonded over its length to the piston wall at each thin segment and extends in length from adjacent the thickened portion circumferential boundary to adjacent its nearby boss.

The inserts can be bonded to fiat inside surface portions of the piston. The inserts can be provided with openings therein and said openings can be cast full of metal which is integral with the piston and secures the inserts to the piston. Best results are obtained if all of the inserts are of the same material and of the same form, so that each of the inserts has the same thermal expansion.

The invention is further described in reference to the accompanying drawing, wherein:

FIG. 1 is an elevation view in cross-section of a piston according to the invention; and

FIG. 2 is a plan view in cross-section taken along line 22 in FIG. 1.

The piston comprises a top member 11, a ring receiving portion 12 depending from the top member, and a skirt 13 depending from the ring receiving member and extending to the bottom of the piston. The piston is an integral casting and is formed with bosses 3 having the bracing 3a. The piston is oval as is discussed above, and includes diametrically opposed circumferentially extending segments 5 intermediate the wrist pin bosses, which are relatively thick. The wall segments 1 which are each disposed intermediate the thick section and a wrist pin, are relatively thin. An insert 2 is positioned at each of the pin segments 1 and the length of the insert extends from a circumferential boundary of the thickened portion to adjacent the nearby boss. The inserts 2 extend in length from the thick segment and, preferably, extend to Within the thickened segment. The adjacent ends of the inserts, however, are spaced so as to leave a portion of the thick segment free of insert length. The length of the thickened section can be about equal to the length of one of the inserts.

The thick segments 5 preferably extend over the entire length of the piston skirt 13, and the inserts are disposed, preferably, over a relatively short length of the skirt 13, and adjacent the upper part thereof.

The inserts and the piston wall provide a series of bimetallic elements disposed at spaced intervals about the piston wall. The forces arising at the interface of the inserts and the piston wall are not great, and the inserts can be retained in place by providing therein openings of rectangular, quadrangular, or round form, and casting within these openings metal which is provided integral with the metal of the piston wall. The openings in the inserts are preferably all of the same shape and the openings are symmetrically arranged so that uniform deformation will result upon heating. Further, the piston is preferably free of beads or other reinforcement ribs in the area of the inserts, since such reinforcement would tend to distort the curvature of the bi-metallic elements.

Instead of securing the insert in place as just described,

the inserts can'be secured to the piston wall by molecular bonding.

The inserts, which are plate-like strips, should not pass through the pin bosses as the lower thermal expansion of the first would result in internal tensions which would reduce the strength of the piston as 'a whole.

The four vbi-metallic elements or compensating zones about the piston skirt are thus provided so that these elements are independe'ntof one another.

By extending the thickened portions 5 over the entire length orsubstantially the entire length of the skirt 13,

unequal curvatures in the 'fourindividual compensating members can be compensated for, andthus the original shape of the segments 5 can be preserved during the corn pensating action 1 In the embodiment shown in the drawing, the inserts 2 are provided with rectangular openings 2a and metal i which is integral with the piston wall fills these openings.

' The-inserts project-a short way into the bosses 3;

The piston can be a cast of light weight metal having a relatively large thermal expansion (coeflicient of thermal expansion), as is well known in the art, and, similar-' ly, the inserts can be of ferrous metal, for example steel, as is well known in-theart.

While the invention has been described with respect to particular embodiments thereof, various modifications will occur to those skilled in the art, and it is desired to secure by these Letters Patent all such modifications a ments between said thick segment" and the wrist pin expansion bonded over its ,length to the piston wall at each thin segment and extending in length from the thickened portion to adjacent its nearby boss, the adjacent ends of the inserts being spaced leaving a portion of the thick segment free of insert, length.

3. An oval piston comprising'a hollow piston body of a light material of relatively large thermal expansion and having'a top member and a wall depending from the top member and including .a skirt extending to termination at the bottom of the-piston, Wrist pin bosses joined to the skirt and for receiving a Wrist pin for the piston, two diametrically opposed circumferentially extending segments of the piston wall "disposed intermediate the wrist pin bosses and extending substantially over the-entire length of said'skirjt being relatively thick, a relatively thin circumferentially extending 'wall segment between each circumferential boundary of each thick segment and the nearby wrist pinboss, an insert of material of relatively small'thermal expansion bonded over its length'to the piston wall at each thin segment and extending in length from adjacent the thickened portion circumferential boundary to adjacent its nearby boss.

4. An oval piston comprising a hollow piston body of a light metal of relatively-large thermal expansion and having a top member and a wall depending from the top member and including a skirt extending to termination at thebottom of the piston, wrist pin bosses joinedto the skirt and for receiving a wristvpinfor the piston, two

diametrically opposed circumferentially extending segments of thepiston wall disposed intermediate the wrist pin bosses and extending substantially over'the entire length of said skirt being-relatively thick, a relatively thin 'circumferentiallyextending wall segment between thick, relatively thin circumferentially extending wall segbosses, one thin -segment'on each side of said'thick seg- 7 having a top member and a wall depending from the top member and including a skirt extending to termina ,tion at the bottomof the piston, wrist pin bossesjoined to'the skirt and for receiving'a wrist pin for the piston, a

circumferentially extending segment of the piston wall intermediate the wrist pin bosses and extending substantially over the entire length of said skirt being relatively thick, relatively'thin circumfe'rentially extending wall segments between said thick segment and-the wrist pin bosses, one thin segment on each side of said thick segment, an insert of material of relatively small therma'I 6. An oval piston according to claim 5, said inserts having means defining openingstherein, said openingsbeing cast full of metal integral with the piston and securirig the inserts to the piston.- d

7. An oval piston according to claim 4, all of said inserts being of the same material and thesame form whereby each'of the inserts has the same thermal expansion; I

8. An'ovalpiston according to claim 4, said inserts extending overa relatively short length of said skirt adjacent the upper part thereof. 1

References Cited in thefile of this patent UNITED STATES PATENTS 1,868,144 Hcinz e ]uly*19, 1932 2,086,677, Nelson July 13, 1937 2,911,269 lubel Nov. 3, 1959 

1. AN OVAL PISTON COMPRISING A HOLLOW PISTON BODY OF A LIGHT METAL OF RELATIVELY LARGE THERMAL EXPANSION AND HAVING A TOP MEMBER AND A WALL DEPENDING FROM THE TOP MEMBER AND INCLUDING A SKIRT EXTENDING TO TERMINATION AT THE BOTTOM OF THE PISTON, WRIST PIN BOSSES JOINED TO THE SKIRT AND FOR RECEIVING A WRIST PIN FOR THE PISTON, A CIRCUMFERENTIALLY EXTENDING SEGMENT OF THE PISTON WALL INTERMEDIATE THE WRIST PIN BOSSES AND EXTENDING SUBSTANTIALLY OVER THE ENTIRE LENGTH OF SAID SKIRT BEING RELATIVELY THICK, RELATIVELY THIN CIRCUMFERENTIALLY EXTENDING WALL SEGMENTS BETWEEN SAID THICK SEGMENT AND THE WRIST PIN BOSSES, ONE THIN SEGMENT ON EACH SIDE OF SAID THICK SEGMENT, AN INSERT OF MATERIAL OF RELATIVELY SMALL THERMAL EXPANSION BONDED OVER ITS LENGTH TO THE PISTON WALL AT EACH THIN SEGMENT AND EXTENDING IN LENGHT FROM ADJACENT THE THICKENED PORTION CIRCUMFERENTIAL BOUNDARY TO ADJACENT ITS NEARBY BOSS. 